Walrein and Aqua Energy Question

[plaidlesspez]

Hoe does Walrein's Hydro Reverse attack work with Aqua Energy? Does the energy just satisfy the energy cost to perform the attack? Or can you move the card back to your hand and do an extra 20 damage? I'm pretty sure it just provides energy for the attacks energy cost, but I just wanted to make sure. Also, what about with DRE?

 

[BJJ763]

Aqua Energy would only pay for the cost of the attack. Hydro Reverse only returns basic W energy cards back to your hand.